The Bishop Museum goes mad over science with our third annual Mad About Science Day on March 31. This popular festival showcases all types of science, from astronomy, archaeology, and marine studies to volcanology and more.

Learn about the health of our planet with our global warming exhibits and presentations, as well as the health of your body with activities from the UH medical school. Biodiesel expert Kyle Datta will speak on global warming at 11 a.m. and 2 p.m, and the museum's Natural Sciences Department will give behind-the-scenes tours between 1 and 3:30 p.m. The festival runs from 9 a.m. to 9 p.m.

The Hawaiian Astronomical Society and the UH Institute for Astronomy will be on the grounds providing telescopes during the day to view the sun and at night to view the stars. Other participants include local environmental organizations providing information on recycling and conservation. Activities and demonstrations will be ongoing throughout the day and evening but some are limited to available seating, so make sure you get your tickets for those programs at the Information Tent as soon as you arrive.

Admission for Mad About Science is $3; museum members and children under 3 years get in free.

ECLIPSE AND EQUINOX

A total lunar eclipse will be visible on Saturday from parts of all seven continents. But Hawai'i is not included — either in continent status or in viewing the eclipse. I don't usually like to dwell on events we cannot see in Hawai'i, but because eclipses usually get publicized through the media many people become aware of the event but may miss out on the details. This is also a good opportunity to talk about the patterns responsible for eclipses.

The reason we cannot see this month's lunar eclipse is simple — we just happen to be in the portion of the Earth that will miss the entire event. By the time the last bit of the Earth's shadow has passed by the moon, Hawai'i will have not yet seen the full moon rise above the horizon.

In some past cultures, eclipses were seen as omens and as signaling the presence of mythical creatures in the heavens. Today we know that eclipses are caused by the alignment of the sun, moon and Earth in space.

Most people know how solar and lunar eclipses happen but are not always sure why we can't always see them, or why we don't have them more frequently. After all, the moon passes between the sun and Earth at least once a month, and likewise the Earth is between the sun and moon as many times. I touched on this topic last November during the Mercury transit, involving nodes, the points of orbit intersection.

The plane of the moon's orbit around the Earth isn't on the same plane as the Earth's orbit around the sun. If it were, we would see eclipses every month as the moon lines up exactly at full and new moon phases. The moon's orbit is tilted slightly, about 5 degrees, so most of the time the shadows of the moon and Earth miss each other. But the planes of the orbits intersect at the two points called nodes, and it is at these points that eclipses can occur if the Earth and its companion are in the same place at the same time in respect to the sun.

This alignment produces an "eclipse season" of about a month when eclipses are possible, twice a year at each of the two node points. At this time, either lunar or solar eclipses can take place as the moon revolves around the Earth during the month.

March also brings a partial solar eclipse to Earth, but that eclipse will only be visible in eastern Asia and Russia and parts of northern Alaska.

The plane of the Earth's orbit is called the ecliptic and if you haven't guessed, it is related to the word eclipse for that very reason.

So although we will miss this season's lunar eclipse, we will have another opportunity as we pass through the other node. Hawai'i will be lucky then, as we will be directly in the path of a total lunar eclipse in August.

Now, what about the equinox? That too, is related to the ecliptic. No matter what the groundhog says, the equinox signals the first day of spring, whether we're ready for it or not.

As the Earth travels around the sun, it appears the sun moves slowly through the stars. This is not to be confused with the daily sunrise and sunset motion caused by the Earth's rotation, but the annual movement of the sun through the constellations (called the zodiac) that lie on the ecliptic. This imaginary line crosses another imaginary line called the celestial equator, or the Earth's equator projected into the sky. (Again, nodes.) At these points are the vernal and autumnal equinoxes, in March and September.

This year's vernal equinox will fall on March 20 at 2:07 p.m. in Hawai'i.

THE PLANETS